http://jacksonupperco.com/2016/02/16/the-ten-best-cheers-episodes-of-season-five/

Was Cheers Season 5 The Worst Season? (https://tvovermind.com/cheers-season-5-worst-season/)

Maybe the writers of Cheers were bitter over losing her, or maybe the writers just didn’t like the Diane character, but she goes out on a low note in Cheers‘ fifth season. Just the way she brutally humiliated Sam over and over again when he proposed was enough to drag the show down on an episode-to-episode basis; but once she took him to court and created a massive scene in “Chambers vs. Malone”, which really only pointed out how toxic their romantic relationship had become over five seasons of on-again, off-again. As the turning point for the entire season (as the 13th episode, “Chambers vs. Malone” is literally the halfway mark), everything in the emotional resolutions to follow in the next thirteen episodes are scarred by the previous thirteen, which reduced Sam to a frustrated, sniveling bartender and Diane to a selfish, completely self-indulgent and over-demanding waitress, removing any of the charm and allure that made her annoying tendencies endearing – or at the very least, comedic.